Macromolecular insoluble cold globulin (MICG): a marker for pluripotential hemopoietic stem cells.

In embryonic mice pluripotential hemopoietic stem cells (PHSC) originate in the yolk sac and migrate to the fetal liver and from there to the bone marrow. Hemopoietic cells from yolk sac and fetal liver also migrate to the thymic primordium, and within the thymic environment these prothymocytes differentiate into mature T cells. We have recently demonstrated that macromolecular insoluble cold globulin (MICG), a T cell marker, is synthesized and inserted into the plasma membrane of embryonic prothymocytes as soon as these cells appear in the early thymus. In addition, we have shown that MICG+ cells are present within the fetal liver before the thymus has fully formed. In the present study we show that pluripotential hemopoietic stem cells in the fetal liver and bone marrow have MICG on their surface and represent a subpopulation of these MICG+ cells. The implications of these findings in relationship to stem cell differentiation and isolation are discussed.